The abundance of therapeutic targets of drug candidates and of combinatorial and computational technologies has created a demand for laboratory automation of mix-and-measure assays (chemical reaction tests). To increase laboratory productivity and reduce costs, a clear trend towards assay miniaturization, parallelization, and higher throughput has emerged. Traditional approaches to low-volume liquid handling technologies range from classical liquid handlers employing syringe-based dispensing to piezo-electric dispensers. Some offer a fixed volume at the expense of accuracy and precision while others promote a variable volume range at the expense of delivery or dead volume. Most of the pressure syringe-based systems as well as solenoid valve mechanism based systems are not well suited to dispense liquids in nano- to low-micro-liters volume range with great precision, as is required for assay miniaturization demanded by high throughput screening. These traditional dispenser technologies generally comprise an assembly of discrete components, including one nozzle per assembly. Dispensing from a single nozzle can be slow. To compensate partly for the slow throughput performance these single-nozzle dispensers can be multiplexed by adding one or more additional assemblies of discrete components.
An inkjet printer typically includes one or more cartridges that contain ink. In some designs, the cartridge has discrete reservoirs of more than one color of ink. Each reservoir is connected via a conduit to a print head that is mounted to the body of the cartridge. The print head is controlled for ejecting minute drops of ink from the print head to a printing medium, such as a paper which is advanced through the printer. The print head is usually scanned across the width of the paper. The paper is advanced, between print head scans, in a direction parallel to the length of the paper.
The mechanism for expelling ink drops from each ink chamber (known as a “drop generator”) includes a heat transducer, which typically includes a thin-film resistor. The resistor is carried on an insulated substrate, such as a silicon die. The resistor has conductive traces attached to it so that the resistor can be selectively driven (heated) with pulses of electrical current. The heat from the resistor is sufficient to form a vapor bubble in each ink chamber. The rapid expansion of the bubble propels an ink drop through the nozzle that is adjacent to the ink chamber.